Dual channel material for finFET for high performance CMOS

ABSTRACT

Silicon fins are formed in a bulk silicon substrate and thereafter trench isolation regions are formed between each silicon fin. The silicon fins in nFET and pFET device regions are then recessed. A relaxed silicon germanium alloy fin portion is formed on a topmost surface of each recessed silicon fin portion or on exposed surface of the substrate. A compressively strained silicon germanium alloy fin portion is formed on each relaxed silicon germanium alloy fin portion within the pFET device region, and a strained silicon-containing fin portion is formed on each relaxed silicon germanium alloy fin portion within the nFET device region. Sidewall surfaces of each compressively strained silicon-containing germanium alloy fin portion and each tensile strained silicon-containing fin portion are then exposed. A functional gate structure is provided on the exposed sidewall surfaces of each compressively strained silicon-containing germanium alloy fin portion and each tensile strained silicon-containing fin portion.

BACKGROUND

The present application relates to a non-planar semiconductor structureand a method of forming the same. More particularly, the presentapplication relates to a semiconductor structure containing tensilestrained silicon-containing fins for n-type FETs and compressivestrained silicon germanium alloy fins for p-type FETs.

For more than three decades, the continued miniaturization of metaloxide semiconductor field effect transistors (MOSFETs) has driven theworldwide semiconductor industry. Various showstoppers to continuedscaling have been predicated for decades, but a history of innovationhas sustained Moore's Law in spite of many challenges. However, thereare growing signs today that metal oxide semiconductor transistors arebeginning to reach their traditional scaling limits. Since it has becomeincreasingly difficult to improve MOSFETs and therefore complementarymetal oxide semiconductor (CMOS) performance through continued scaling,further methods for improving performance in addition to scaling havebecome critical.

The use of non-planar semiconductor devices such as, for example,semiconductor fin field effect transistors (finFETs) is the next step inthe evolution of complementary metal oxide semiconductor (CMOS) devices.Semiconductor fin field effect transistors (FETs) can achieve higherdrive currents with increasingly smaller dimensions as compared toconventional planar FETs. In order to extend these devices for multipletechnology nodes, there is a need to boost the performance with highmobility channels and stressor elements.

SUMMARY

Silicon fins are formed in a bulk silicon substrate and thereaftertrench isolation regions are formed between each silicon fin. Thesilicon fins in nFET and pFET device regions are then recessed. Arelaxed silicon germanium alloy fin portion is formed on a topmostsurface of each recessed silicon fin portion or on exposed surface ofthe substrate. A compressively strained silicon germanium alloy finportion is formed on each relaxed silicon germanium alloy fin portionwithin the pFET device region, and a tensile strained silicon-containingfin portion is formed on each relaxed silicon germanium alloy finportion within the nFET device region. Sidewall surfaces of eachcompressively strained silicon-containing germanium alloy fin portionand each tensile strained silicon-containing fin portion are thenexposed. A functional gate structure is provided on the exposed sidewallsurfaces of each compressively strained silicon-containing germaniumalloy fin portion and each tensile strained silicon-containing finportion.

In one aspect of the present application, a method of forming asemiconductor structure containing tensile strained silicon-containingfins for n-type FETs and compressive strained silicon-containinggermanium alloy fins for p-type FETs is provided. The method of thepresent application includes forming a plurality of silicon finsextending upwards from a bulk silicon portion, wherein each silicon finof the plurality of silicon fins is separated by a trench isolationregion. A predetermined number of silicon fins of the plurality ofsilicon fins are then recessed to expose a surface of the bulk siliconportion in an nFET device region and a pFET device region of the bulksilicon portion or to provide a plurality of silicon fin portions in annFET device region and a pFET device region of the bulk silicon portion.A relaxed silicon germanium alloy fin portion is formed on a topmostsurface of each silicon fin portion or the exposed surface of the bulksilicon portion. A compressively strained silicon-containing germaniumalloy fin portion is formed on a topmost surface of each relaxed silicongermanium alloy fin portion in the pFET device region and a tensilestrained silicon-containing fin portion is formed on a topmost surfaceof each relaxed silicon germanium alloy fin portion in the nFET deviceregion. Each trench isolation region is recessed to provide trenchisolation structures that partially expose sidewall surfaces of eachcompressively strained silicon-containing germanium alloy fin portionand each tensile stained silicon fin portion.

In another aspect of the present application, a semiconductor structurethat contains tensile strained silicon-containing fins for n-type FETsand compressive strained silicon-containing germanium alloy fins forp-type FETs is provided. The semiconductor structure of the presentapplication includes a bulk silicon portion comprising an nFET deviceregion and a pFET device region. A pFET fin stack extends upward from asurface of the bulk silicon portion within the pFET device region andcomprises, from bottom to top, a relaxed silicon germanium alloy finportion and a compressively strained silicon-containing germanium alloyfin portion. An nFET fin stack extends upward from another surface ofthe bulk silicon portion within the nFET device region and comprises,from bottom to top, a relaxed silicon germanium alloy fin portion and atensile strained silicon-containing fin portion. A first set of trenchisolation structures is located adjacent the pFET fin stack, whereineach of the first set of trench isolation structures covers entiresidewall surfaces of the relaxed silicon germanium alloy fin portion anda portion, but not all, of sidewall surfaces of the compressivelystrained silicon-containing germanium alloy fin portion. A second set oftrench isolation structures is adjacent the nFET fin stack, wherein eachof the second set of trench isolation structures covers entire sidewallsurfaces of the relaxed silicon germanium alloy fin portion and aportion, but not all, of sidewall surfaces of the tensile strainedsilicon-containing fin portion.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a cross sectional view of a first exemplary semiconductorstructure comprising a hard mask layer located on an exposed topmostsurface of a bulk silicon substrate that can be employed in oneembodiment of the present application.

FIG. 2 is a cross sectional view of the first exemplary semiconductorstructure of FIG. 1 after formation of a plurality of silicon fins thatare capped with a remaining portion of the hard mask layer and formationof trench isolation regions.

FIG. 3 is a cross sectional view of the first exemplary semiconductorstructure of FIG. 2 after selectively removing the remaining hard masklayer portions and recessing exposed silicon fins from a predeterminedarea of the structure.

FIG. 4 is a cross sectional view of the first exemplary semiconductorstructure of FIG. 3 after forming a relaxed silicon germanium alloy finportion on a topmost surface of each recessed silicon fin.

FIG. 5 is a cross sectional view of the first exemplary semiconductorstructure of FIG. 4 after forming a compressively strainedsilicon-containing germanium alloy fin portion on a topmost surface ofthe relaxed silicon germanium alloy fin portion within a pFET deviceregion of the structure.

FIG. 6 is a cross sectional view of the first exemplary semiconductorstructure of FIG. 5 after forming a tensile strained silicon-containingfin portion on a topmost surface of the relaxed silicon germanium alloyportion within an nFET device region of the structure.

FIG. 7 is a cross sectional view of the first exemplary semiconductorstructure shown in FIG. 6 after recessing the trench isolation regions.

FIG. 8 is a cross sectional view of the first exemplary semiconductorstructure of FIG. 7 after forming of a gate structure in each defineregion of the structure.

DETAILED DESCRIPTION

The present application will now be described in greater detail byreferring to the following discussion and drawings that accompany thepresent application. It is noted that the drawings of the presentapplication are provided for illustrative purposes only and, as such,the drawings are not drawn to scale. It is also noted that like andcorresponding elements in the various embodiments of the presentapplication are referred to by like reference numerals.

In the following description, numerous specific details are set forth,such as particular structures, components, materials, dimensions,processing steps and techniques, in order to provide an understanding ofthe various embodiments of the present application. However, it will beappreciated by one of ordinary skill in the art that the variousembodiments of the present application may be practiced without thesespecific details. In other instances, well-known structures orprocessing steps have not been described in detail in order to avoidobscuring the present application.

In one aspect of the present application, a non-planar semiconductorstructure is provided that comprises tensile strained silicon-containingfins for n-type FETs and compressive strained silicon-containinggermanium alloy fins for p-type FETs on a semiconductor substrate forhigh performance CMOS devices, while maintaining a region of unstrainedsilicon-containing for lower performance devices. In another aspect ofthe present application, a method of forming such a non-planarsemiconductor structure is provided.

Referring first to FIG. 1, there is illustrated a first exemplarysemiconductor structure that can be employed in accordance with anembodiment of the present application. Specifically, the first exemplarysemiconductor structure shown in FIG. 1 comprises a hard mask layer 12Llocated on a topmost surface of a bulk silicon substrate 10L. The term“bulk” as used in conjunction with the phrase “silicon substrate”denotes that the entire substrate is comprised of silicon.

In some embodiments of the present application, the bulk siliconsubstrate 10L may be single crystalline silicon. In other embodiments ofthe present application, the bulk silicon substrate 10L may bepolycrystalline silicon or amorphous silicon. The crystal orientation ofthe bulk silicon substrate 10L may be {100}, {110}, or {111}. Othercrystallographic orientations besides those specifically mentioned canalso be used in the present application.

The hard mask layer 12L that is present on a topmost surface of the bulksilicon substrate 10L is a contiguous layer that covers the entirety ofthe topmost surface of the bulk silicon substrate 10L. The hard masklayer 12L that is employed in the present application may include asemiconductor oxide, a semiconductor nitride and/or a semiconductoroxynitride. In one embodiment, the hard mask material that can be usedin providing the hard mask layer 12L can be comprised of silicondioxide. In another embodiment, the hard mask material that can be usedin providing the hard mask layer 12L can be comprised of siliconnitride. In yet another embodiment, the hard mask material that can beused in providing the hard mask layer 12L can be a stack comprised of,in any order, silicon dioxide and silicon nitride.

In some embodiments, the hard mask material that can be used inproviding the hard mask layer 12L can be formed by a deposition processsuch as, for example, chemical vapor deposition (CVD) and plasmaenhanced chemical vapor deposition (PECVD). In other embodiments, thehard mask material that can be used in providing the hard mask layer 12Lcan be formed by a thermal process such as, for example, thermaloxidation and/or thermal nitridation. In yet other embodiments, the hardmask material that can be used in providing the hard mask layer 12L canbe formed by a combination of a deposition process and a thermalprocess. The thickness of the hard mask material that can be used inproviding the hard mask layer 12L can range from 2 nm to 10 nm, with athickness from 3 nm to 6 nm being more typical.

Referring now to FIG. 2, there is illustrated the first exemplarysemiconductor structure of FIG. 1 after formation of a plurality ofsilicon fins 16 that extend upward from a remaining portion of the bulksilicon substrate 10L, and formation of trench isolation regions 14.Each trench isolation region 14 is located adjacent a silicon fin of theplurality of silicon fins. The remaining portion of the bulk siliconsubstrate can be referred to herein as a bulk silicon portion 10. Atopmost surface of each silicon fin 16 is capped with a remainingportion of the hard mask layer 12L. The remaining portion of the hardmask layer that is present on a topmost surface of each silicon fin 16can be referred to herein as hard mask cap 12.

As is shown in FIG. 2, the topmost surface of each hard mask cap 12 iscoplanar with a topmost surface of each trench isolation region 14.Also, and since each silicon fin 16 is formed within the bulk siliconsubstrate 10L, no material interface is present between each silicon fin16 and the bulk silicon portion 10. Further, sidewall surfaces of eachsilicon fin 16 are vertically coincident with sidewall surfaces of acorresponding overlying hard mask cap 12.

The plurality of silicon fins 16 can be formed by patterning thematerial stack of the hard mask layer 12L and bulk silicon substrate10L. During the patterning of material stack of the hard mask layer 12Land bulk silicon substrate 10L, a plurality of trenches are formed intothe hard mask layer 12L and the bulk silicon substrate 10L. Each trenchthat is formed extends completely through the hard mask layer 12L butonly partially into the bulk silicon substrate 10L.

As stated above, the plurality of silicon fins and the plurality oftrenches can be defined by a patterning process. In one embodiment, thepatterning process includes a sidewall image transfer (SIT) process. TheSIT process includes forming a contiguous mandrel material layer (notshown) on the topmost surface of the hard mask layer 12L. The contiguousmandrel material layer (not shown) can include any material(semiconductor, dielectric or conductive) that can be selectivelyremoved from the structure during a subsequently performed etchingprocess. In one embodiment, the contiguous mandrel material layer (notshown) may be composed of amorphous silicon or polysilicon. In anotherembodiment, the contiguous mandrel material layer (not shown) may becomposed of a metal such as, for example, Al, W, or Cu. The contiguousmandrel material layer (not shown) can be formed, for example, bychemical vapor deposition or plasma enhanced chemical vapor deposition.The thickness of the contiguous mandrel material layer (not shown) canbe from 50 nm to 300 nm, although lesser and greater thicknesses canalso be employed. Following deposition of the contiguous mandrelmaterial layer (not shown), the contiguous mandrel material layer (notshown) can be patterned by lithography and etching to form a pluralityof mandrel structures (also not shown) on the surface of the hard masklayer 12L.

The SIT process continues by forming a dielectric spacer on eachsidewall of each mandrel structure. The dielectric spacer can be formedby deposition of a dielectric spacer material and then etching thedeposited dielectric spacer material. The dielectric spacer material maycomprise any dielectric spacer material such as, for example, silicondioxide, silicon nitride or a dielectric metal oxide. Examples ofdeposition processes that can be used in providing the dielectric spacermaterial include, for example, chemical vapor deposition (CVD), plasmaenhanced chemical vapor deposition (PECVD), and atomic layer deposition(ALD). Examples of etching that be used in providing the dielectricspacers include any etching process such as, for example, reactive ionetching. Since the dielectric spacers are used in the SIT process as anetch mask, the width of the each dielectric spacer determines the widthof each silicon fin.

After formation of the dielectric spacers, the SIT process continues byremoving each mandrel structure. Each mandrel structure can be removedby an etching process that is selective for removing the mandrelmaterial as compared to the material of the dielectric spacers and hardmask layer 12L. Following the mandrel structure removal, the SIT processcontinues by transferring the patterned provided by the dielectricspacers into the hard mask layer 12L and then into the bulk siliconsubstrate 10L. The pattern transfer may be achieved by an etchingprocess. Examples of etching processes that can used to transfer thepattern may include dry etching (i.e., reactive ion etching, plasmaetching, ion beam etching or laser ablation) and/or a chemical wet etchprocess. In one example, the etch process used to transfer the patternmay include one or more reactive ion etching steps. Upon completion ofthe pattern transfer, the SIT process concludes by removing thedielectric spacers from the structure. Each dielectric spacer may beremoved by etching or a planarization process.

During the patterning process a plurality of trenches is also formedinto the hard mask layer 12L and the bulk silicon substrate 10L, eachtrench is the filled with a trench dielectric material such as, forexample, an oxide. Optionally, a liner may be formed in each trenchprior to trench fill, a densification step may be performed after thetrench fill and a planarization process may follow the trench fill aswell. The trenches that are processed in this manner provide the trenchisolation regions 14. Each trench isolation region 14 is locatedadjacent to a silicon fin 16.

As used herein, a “fin” refers to a contiguous structure including asemiconductor material, in the present case silicon, and including apair of vertical sidewalls that are parallel to each other. As usedherein, a surface is “vertical” if there exists a vertical plane fromwhich the surface does not deviate by more than three times the rootmean square roughness of the surface. Each silicon fin 16 that is formedis comprised of unstrained silicon-containing.

In one embodiment of the present application, each silicon fin 16 has aheight from 10 nm to 100 nm, and a width from 4 nm to 30 nm. In anotherembodiment of the present application, each silicon fin 16 has a heightfrom 15 nm to 50 nm, and a width from 5 nm to 12 nm. Each silicon fin 16is spaced apart from its nearest neighboring silicon fin 16 by the widthof the trench isolation region 14 that is present between the twosilicon fins 16. Also, each silicon fin 16 is oriented parallel to eachother.

Referring now to FIG. 3, there is illustrated the first exemplarysemiconductor structure of FIG. 2 after selectively removing theremaining hard mask layer portions (i.e., the hard mask cap 12) andrecessing exposed silicon fins 16 from a predetermined area of thestructure. The recessed silicon fins are labeled as element 16 p in thedrawings of the present application. Each recessed silicon fin ishereinafter referred to herein as a silicon fin portion 16 p.

The structure shown in FIG. 3 can be formed by first providing a blockmask 18 on a predetermined area 100 of the structure. The predeterminedarea 100 can be an area in which lower performance devices can besubsequently formed. The block mask 18 can be comprised of a photoresistmaterial, a hard mask material that differs from that of the hard maskmaterial that provides the hard mask layer 12L and each hard mask cap12, or a combination thereof. The block mask 18 can be formed bydeposition and patterning. The patterning may include only lithographyor a combination of lithography and etching can be used in defining theblock mask 18.

After forming block mask 18 on the predetermined area 100 of thestructure, the exposed hard mask caps 12 that are not protected, i.e.,covered, by the block mask 18, are removed from each of the silicon fins16. The removal of the exposed hard mask caps 12 can be performedutilizing a selective etching process. By “selective etching” it ismeant an etching process that removes one material at a greater ratethan other materials. In one example and when hard mask layer 12L issilicon nitride, and the trench dielectric material is silicon dioxide,and the block mask 18 is also silicon dioxide, hot phosphoric acid canbe employed to remove the exposed hard mask caps 12 that are notprotected by block mask 18.

The selective removal of the exposed hard mask caps 12 exposes a topmostsurface of each silicon fin 16 in the area of the structure notprotected by the block mask 18. Each exposed fin structure 16 is thenrecessed utilizing an etching process that is selective in removingsilicon. In one embodiment, a reactive ion etch (i.e., RIE) can be usedto recess each silicon fin 16 that is not protected by the block mask18. In some embodiments (as shown), the exposed silicon fins 16 arepartially recessed. In other embodiments (not shown), the entirety ofexposed silicon fins 16 is removed to expose a surface of the bulksilicon portion 10.

Each silicon fin portion 16 p that is formed has a height that is lessthan the height of the remaining silicon fins 16 that are protected bythe block mask 18. In one embodiment, the height of each silicon finportion 16 p is greater than 0 nm to 10 nm. Other heights for thesilicon fin portions 16 p are possible so long as the height of siliconfin portion 16 p is less than the height of the remaining silicon fins16 that are protected by the block mask 18. In accordance with thepresent application, each silicon fin portion 16 p has a topmost surfacethat is vertically offset and located above a bottommost surface of eachtrench isolation region 14.

Referring now to FIG. 4, there is illustrated the first exemplarysemiconductor structure of FIG. 3 after forming a relaxed silicongermanium alloy fin portion 20 on a topmost surface of each silicon finportion 16 p. In embodiments in which the entire silicon fin isrecessed, the relaxed silicon germanium alloy fin portion 20 is formedon the exposed surface of bulk silicon portion 10. During the formationof the relaxed silicon germanium alloy fin portion 20, block mask 18remains in predetermined area 100. The formation of a relaxed silicongermanium alloy fin portion 20 on topmost surface of each silicon finportion 16 p (or the exposed surface of bulk silicon portion 10)provides a bilayer lattice mismatched heterostructure in the area of thestructure not protected by the block mask 18.

The term “relaxed silicon germanium alloy” is used throughout thepresent application to denote a silicon germanium alloy material thathas a relaxation value of 90% or greater. Each relaxed silicon germaniumalloy fin portion 20 that is formed can have a germanium content of 20atomic percent or greater and the remainder being silicon. Each relaxedsilicon germanium alloy portion 20 may be compositional graded orcompositional ungraded.

Each relaxed silicon germanium alloy fin portion 20 that is formed has abottommost surface that directly contacts the topmost surface of acorresponding silicon fin portion 16 p or an exposed surface of the bulksilicon portion 10, and a topmost surface that is located beneath atopmost surface of each silicon fin 16 that is protected by block mask18. The height of each relaxed silicon germanium alloy fin portion 20has to be greater than the critical thickness of the respective silicongermanium concentration of 20 atomic percent germanium to allow fullrelaxation. In the embodiment that is illustrated, each relaxed silicongermanium alloy fin portion 20 has sidewall surfaces that are verticallycoincident with sidewall surfaces of the silicon fin portion 16 p.

Each relaxed silicon germanium alloy fin portion 20 that is formedincludes a lower portion (indicated by “χ” in the drawings) having afirst defect density and an upper portion (not including the “χ”) havinga second defect density that is less than the first defect density.

Each relaxed silicon germanium alloy fin portion 20 that is provided canbe formed utilizing an epitaxial semiconductor regrowth process such asis described, for example, in U.S. Patent Application Publication No.2011/0049568 to Lochtefeld et al., the entire content and disclosure ofwhich is incorporated herein by reference. Notably, and since anepitaxial semiconductor regrowth process is used in forming each relaxedsilicon germanium alloy fin portion 20, each relaxed silicon germaniumalloy fin portion 20 has a same crystalline characteristic as thesemiconductor material of the deposition surface. Thus, in the presentapplication, each relaxed silicon germanium alloy fin portion 20 has anepitaxial relationship, i.e., same crystal orientation, with theunderlying silicon fin portion 16 p or the underlying exposed surface ofthe bulk silicon portion 10.

In some embodiments of the present application, the selectedcrystallographic direction of the relaxed silicon germanium alloy finportion 20 is aligned with at least one propagation direction ofthreading dislocations in the opening in which each relaxed silicongermanium alloy fin portion 20 is formed. Threading dislocations in thisregion may substantially terminate at the sidewall of the neighboringtrench isolation regions 14. In one embodiment of the presentapplication, the selected crystallographic direction of the silicon finportion 16 p is aligned with direction of propagation of threadingdislocations in each relaxed silicon germanium alloy fin portion 20. Incertain embodiments, the orientation angle ranges from about 30 to about60 degrees, for example, is about 45 degrees to such crystallographicdirection. As mentioned above, the surface of the semiconductor layermay have (100), (110), or (111) crystallographic orientation. In someembodiments, the selected crystallographic direction is substantiallyaligned with a <110> crystallographic direction of the silicon finportion 16 p.

Each relaxed silicon germanium alloy fin portion 20 can be formed byselective epitaxial growth in any suitable epitaxial deposition system,including, but not limited to, atmospheric-pres sure CVD (APCVD), low-(or reduced-) pressure CVD (LPCVD), ultra-high-vacuum CVD (UHVCVD), bymolecular beam epitaxy (MBE), metal-organic CVD (MOCVD) or by atomiclayer deposition (ALD). In the CVD process, selective epitaxial growthtypically includes introducing a source gas into the chamber. The sourcegas may include at least one precursor gas and a carrier gas, such as,for example hydrogen. The reactor chamber is heated, such as, forexample, by RF-heating. The growth temperature in the chamber may rangefrom 250° C. to 900° C. The growth system also may utilize low-energyplasma to enhance the layer growth kinetics. The epitaxial growth systemmay be a single-wafer or multiple-wafer batch reactor.

Referring now to FIG. 5, there is illustrated the first exemplarysemiconductor structure of FIG. 4 after forming a compressively strainedsilicon-containing germanium alloy fin portion 24 on a topmost surfaceof each relaxed silicon germanium alloy fin portion 20 within a pFETdevice region 102 of the structure. The term “compressively strainedsilicon-containing germanium alloy” is used throughout the presentapplication to denote a silicon germanium material having an unstrained(relaxed) lattice constant which is larger than the unstrained latticeconstant of the underlying relaxed silicon germanium alloy fin portion20. Thus, the compressively strained silicon-containing germanium alloyfin portion 24 must have a larger amount of germanium than theunderlying relaxed silicon germanium alloy fin portion 20. Eachcompressively strained silicon-containing germanium alloy fin portion 24may be compositional graded or compositional ungraded. Since thecompressively strained silicon-containing germanium alloy fin portion 24is grown from the surface of the relaxed silicon germanium alloy finportion 20, the compressively strained silicon-containing germaniumalloy fin portion 24 will grow with a lattice constant that is the sameas the relaxed silicon germanium alloy fin portion 20, leading to acompressive strain in the material. The strained silicon-containinggermanium material must be below the critical thickness to maintain thestrain and not to relax.

Each compressively strained silicon-containing germanium alloy finportion 24 that is formed has a bottommost surface that directlycontacts the topmost surface of a relaxed silicon germanium alloy finportion 20, and a topmost surface that is coplanar with a topmostsurface of each hard mask cap 12 that is protected by block mask 18 anda topmost surface of each trench isolation region 14. Each compressivelystrained silicon-containing germanium alloy fin portion 24 that isformed has an epitaxial relationship, i.e., same crystal orientation,with the underlying relaxed silicon germanium alloy fin portion 20.

Each compressively strained silicon-containing germanium alloy finportion 24 has sidewall surfaces that are vertically coincident withsidewall surfaces of the relaxed silicon germanium alloy fin portion 20and, if present, sidewall surfaces of the silicon fin portion 16 p.Collectively and in one embodiment, a vertical stack of, from bottom totop, a single silicon fin portion 16 p, a single relaxed silicongermanium alloy fin portion 20, and a single compressively strainedsilicon-containing germanium alloy fin portion 24 provides a pFET finstack of the present application. Collectively and in anotherembodiment, a vertical stack of, from bottom to top, a single relaxedsilicon germanium alloy fin portion 20, and a single compressivelystrained silicon-containing germanium alloy fin portion 24 provides apFET fin stack of the present application

Each compressively strained silicon-containing germanium alloy finportion 24 is formed by first providing an nFET block mask 22 over thearea 104 of the structure in which nFET devices will be subsequentlyformed. Block mask 18 can remain within the predetermined area 100 ofthe structure. In one embodiment of the present application, nFET blockmask 22 can be comprised of a same block mask material that is used inproviding block mask 18. In another embodiment of the presentapplication, nFET block mask 22 can be comprised of a different blockmask material that is used in providing block mask 18. In one example,block mask 18 may comprise silicon nitride, while block mask 22 maycomprise a photoresist material. nFET block mask 22 can be formedutilizing the processing techniques mentioned above in forming blockmask 18. As is shown, nFET block mask 22 has a bottommost surface thatdirectly contacts the uppermost surface of a relaxed silicon germaniumalloy fin portion 20 within the nFET device region 104.

After providing nFET block mask 22, each compressively strainedsilicon-containing germanium alloy fin portion 24 is formed within thepFET device region 102 that is void of either block mask 18 or nFETblock mask 22. Each compressively strained silicon-containing germaniumalloy fin portion 24 that is formed on the topmost surface of relaxedsilicon germanium alloy fin portion 20 in the pFET device region 102 canbe formed by an epitaxial deposition process.

The terms “epitaxial growth and/or deposition” and “epitaxially formedand/or grown” mean the growth of a semiconductor material on adeposition surface of a semiconductor material, in which thesemiconductor material being grown has the same crystallinecharacteristics as the semiconductor material of the deposition surface.In an epitaxial deposition process, the chemical reactants provided bythe source gases are controlled and the system parameters are set sothat the depositing atoms arrive at the deposition surface of asemiconductor material with sufficient energy to move around on thesurface and orient themselves to the crystal arrangement of the atoms ofthe deposition surface. Therefore, an epitaxial semiconductor materialthat is formed by an epitaxial deposition process has the samecrystalline characteristics as the deposition surface on which it isformed. For example, an epitaxial semiconductor material deposited on a{100} crystal surface will take on a {100} orientation. In someembodiments, epitaxial growth and/or deposition processes are selectiveto forming on a semiconductor surface, and do not deposit material ondielectric surfaces, such as silicon dioxide or silicon nitridesurfaces.

Examples of various epitaxial growth process apparatuses that aresuitable for use in forming epitaxial semiconductor material include,e.g., rapid thermal chemical vapor deposition (RTCVD), low-energy plasmadeposition (LEPD), ultra-high vacuum chemical vapor deposition (UHVCVD),atmospheric pressure chemical vapor deposition (APCVD) and molecularbeam epitaxy (MBE) or metal-organic CVD (MOCVD). The temperature forepitaxial deposition process typically ranges from 250° C. to 900° C.Although higher temperature typically results in faster deposition, thefaster deposition may result in crystal defects and film cracking.

A number of different source gases may be used for the deposition of theeach compressively strained silicon-containing germanium alloy finportion 24. In some embodiments, the source gas for the deposition ofthe each compressively strained silicon-containing germanium alloy finportion 24 include a mixture of a silicon containing gas source and agermanium containing gas source. In other embodiments, the source gasfor the deposition of the each compressively strained silicon-containinggermanium alloy fin portion 24 includes silicon and germanium containingsource gas. Carrier gases like hydrogen, nitrogen, helium and argon canbe used.

After the epitaxial deposition of each compressively strainedsilicon-containing germanium alloy fin portion 24, the nFET block mask22 can be selectively removed from the structure. In one embodiment, andwhen the nFET block mask 22 is comprised of a photoresist material,ashing may be used to remove the photoresist material that provides thenFET block mask 22. In one embodiment, and when the nFET block mask 22is comprised of a hard mask material, an etching process may be used toremove the hard mask material that provides the nFET block mask 22.

Referring now to FIG. 6, there is illustrated the first exemplarysemiconductor structure of FIG. 5 after forming a tensile strainedsilicon-containing fin portion 28 on a topmost surface of each relaxedsilicon germanium alloy fin portion 20 within the nFET device region 104of the structure. The term “tensile strained silicon-containing finportion” is used throughout the present application to denote asilicon-containing material having an unstrained (relaxed) latticeconstant which is smaller than the unstrained lattice constant of theunderlying relaxed silicon germanium alloy fin portion 20. The term“silicon-containing” when used in conjunction with the term tensilestrained silicon-containing fin portion 28 denotes a material thatcontains unalloyed (i.e., pure) silicon, or a silicon germanium alloyhaving a germanium content that is less than the germanium content ofthe relaxed silicon germanium alloy fin portion 20. Since thesilicon-containing material grows from the surface of the relaxedsilicon germanium alloy fin portion 20, the silicon-containing materialwill grow with the lattice constant of the relaxed silicon germaniumalloy fin portion 20, leading to a tensile strain in thesilicon-containing material. The silicon-containing material that isformed must be below the critical thickness to maintain the strain andnot to relax.

Although the present application describes and illustrates the formationof the compressively strained silicon-containing germanium alloy finportion 24 prior to the forming the tensile strained silicon-containingfin portion 28, the order of forming each compressively strainedsilicon-containing germanium alloy fin portion 24 and each tensilestrained silicon-containing fin portion 28 may be reversed. Thus, and insome embodiments, each tensile strained silicon-containing fin portion28 may be formed prior to forming each compressively strainedsilicon-containing germanium alloy fin portion 24.

Each tensile strained silicon-containing fin portion 28 that is formedhas a bottommost surface that directly contacts the topmost surface of arelaxed silicon germanium alloy fin portion 20, and a topmost surfacethat is coplanar with a topmost surface of each hard mask cap 12 that isprotected by block mask 18 and a topmost surface of each trenchisolation region 14. Each tensile strained silicon-containing finportion 28 that is formed has an epitaxial relationship, i.e., samecrystal orientation, with the underlying relaxed silicon germanium alloyfin portion 20.

Each tensile strained silicon-containing fin portion 28 has sidewallsurfaces that are vertically coincident with sidewall surfaces of therelaxed silicon germanium alloy fin portion 20 and, if present, sidewallsurfaces of the silicon fin portion 16 p. Collectively and in oneembodiment, a vertical stack of, from bottom to top, a single siliconfin portion 16 p, a single relaxed silicon germanium alloy fin portion20, and a single tensile strained silicon-containing fin portion 28provides an nFET fin stack of the present application. Collectively andin another embodiment, a vertical stack of, from bottom to top, a singlerelaxed silicon germanium alloy fin portion 20, and a single tensilestrained silicon-containing fin portion 28 provides an nFET fin stack ofthe present application.

Each tensile strained silicon-containing fin portion 28 is formed byfirst providing a pFET block mask 26 over the area 102 of the structurein which pFET devices will be subsequently formed. Block mask 18 canremain within the predetermined area 100 of the structure. In oneembodiment of the present application, pFET block mask 26 can becomprised of a same block mask material that is used in providing blockmask 18. In another embodiment of the present application, pFET blockmask 26 can be comprised of a different block mask material that is usedin providing block mask 18. In one example, block mask 18 may comprisesilicon nitride, while pFET block mask 26 may comprise a photoresistmaterial. pFET block mask 26 can be formed utilizing the processingtechniques mentioned above in forming block mask 18. As is shown, pFETblock mask 26 has a bottommost surface that directly contact theuppermost surface of a compressively strained silicon-containinggermanium alloy fin portion 24 within the pFET device region 102.

After providing pFET block mask 26, each tensile strainedsilicon-containing fin portion 28 is formed within the nFET deviceregion 104 that is void of either block mask 18 or pFET block mask 26.Each tensile strained silicon-containing fin portion 28 that is formedon the topmost surface of relaxed silicon germanium alloy fin portion 20in the nFET device region 104 can be formed by an epitaxial depositionprocess such as that defined above for epitaxially deposition of thecompressively strained silicon-containing germanium alloy fin portion24.

A number of different silicon source gases may be used for thedeposition of the each tensile strained silicon-containing fin portion28. Carrier gases like hydrogen, nitrogen, helium and argon can be used.

After the epitaxial deposition of each tensile strainedsilicon-containing fin portion 28, the nFET block mask 22 and block mask18 can be selectively removed from the structure. Block mask 18 and pFETblock mask 26 can be removed simultaneously or one after the other. Anyconventional block mask material removal process such as, for example,etching, ashing or a combination thereof can be used in removing blockmask 18 and pFET block mask 26 from the structure.

Referring now to FIG. 7, there is illustrated the first exemplarysemiconductor structure shown in FIG. 6 after recessing the trenchisolation regions 14 forming trench isolation structures 14 p. Therecessing process comprises an etching process that is selective inremoving trench dielectric material. In some embodiments, the recessingprocess may also remove the hard mask caps 12 from each silicon fin 16within area 100 of the structure. Alternatively, the hard mask caps 12may be removed in a separate step from the recessing of the trenchisolation regions 14 utilizing another etching process that is selectivein removing the hard mask material that provides each hard mask cap 12.A planarization process such as chemical mechanical planarization mayalso be performed to ensure coplanarity between silicon fins 16,compressively silicon germanium alloy fin portions 24 and tensilestrained silicon-containing fin portions 28 with the various deviceregions 100, 102, and 104.

The aforementioned steps expose a topmost surface of each silicon fin 16within region 100, a topmost surface of each compressively strainedsilicon-containing germanium alloy fin portion 24 of each pFET fin stackwithin pFET device region 102 and a topmost surface of each tensilestrained silicon-containing fin portion 28 of each nFET fin stack withinnFET device region 104.

As is shown, portions of the sidewall surfaces of each silicon fin 16within region 100, portions of the sidewall surfaces of eachcompressively strained silicon-containing germanium alloy fin portion 24of each pFET fin stack within pFET device region 102 and portions of thesidewall surfaces of each tensile strained silicon-containing finportion 28 of each nFET fin stack within nFET device region 104 areexposed. As is also shown, trench isolation structures 14 p remainsurrounding a portion of silicon fin 16 within region 100, a bottommostportion of each compressively strained silicon-containing germaniumalloy fin portion 24 of each pFET fin stack within pFET device region102 and a bottommost portion each tensile strained silicon-containingfin portion 28 of each nFET fin stack within nFET device region 104. Asis further shown, entire sidewall surfaces of each relaxed silicongermanium alloy fin portion 20 and entire sidewall surfaces of eachsilicon fin portion 16 p within the pFET device region 102 and the nFETdevice region 104 are surrounded by a trench isolation structure 14 p.

Referring now to FIG. 8, there is illustrated the first exemplarysemiconductor structure of FIG. 7 after forming of a gate structure ineach device regions, i.e., 100, 102 and 104, of the structure. The gatestructure within device region 100, which may be referred to herein as alow leakage gate structure, is labeled as element 30A and it contains agate dielectric material portion 32A and a gate conductor materialportion 34A. The gate structure within pFET device region 102, which maybe referred to herein as a pFET gate structure, is labeled as element30B and it contains a gate dielectric material portion 32B and a gateconductor material portion 34B. The gate structure within nFET deviceregion 104, which may be referred to herein as an nFET gate structure,is labeled as element 30C and it contains a gate dielectric materialportion 32C and a gate conductor material portion 34C.

As shown, the gate structure 30A surrounds an exposed portion of siliconfin 16 in device region 100, gate structure 30B surrounds an exposedportion of the compressively relaxed silicon germanium fin portion 24within the pFET device region 102, while gate structure 30C surrounds anexposed portion of the tensile strained silicon-containing fin portion28 within the nFET device region 104.

In some embodiments, each gate dielectric material portions 32A, 32B and32C may comprise a same gate dielectric material. In other embodiments,each gate dielectric material portions 32A, 32B and 32C may comprise adifferent gate dielectric material. In yet other embodiments, at leasttwo of gate dielectric material portions 32A, 32B and 32C may comprise asame gate dielectric material, while the other gate dielectric materialportion may comprise a gate dielectric material that is different fromthe two gate dielectric material portions having a same gate dielectricmaterial.

In some embodiments, each gate conductor material portions 34A, 34B and34C may comprise a same gate conductor material. In other embodiments,each gate conductor material portions 34A, 34B and 34C may comprise adifferent gate conductor material. In yet other embodiments, at leasttwo of gate conductor material portions 34A, 34B and 34C may comprise asame gate conductor material, while the other gate conductor materialportions may comprise a gate conductor material that is different fromthe two gate conductor material portions having a same gate conductormaterial.

Gate structures 30A, 30B and 30C can be formed utilizing a gate-firstprocess, a gate-last process or a combination of a gate first processand a gate last process. In a gate first process, the gate structure isformed first followed by the source/drain regions and optionally,merging of each of the source/drain regions.

In a gate last process, the gate structure is formed after source/drainregions are formed. In such a process, a sacrificial gate material isformed straddling an exposed portion of a semiconductor fin, i.e., atleast one of silicon fin 16, compressively strained silicon-containinggermanium alloy fin portion 24 and tensile strained silicon-containingfin portion 28, and on one side of the sacrificial gate structure andthen drain regions can be formed in exposed portions of eachsemiconductor fin and on the other side of the gate. An epitaxial growthprocess can be used to deposit an epitaxial semiconductor material thatcan merge each of the source/drain regions. Next, the sacrificial gatestructure may be replaced with a gate structure as defined above. Thegate structures 30A, 30B and 30C may be referred to as a functional gatestructure. The term “functional gate structure” is used throughout thepresent application as a permanent gate structure used to control outputcurrent (i.e., flow of carriers in the channel) of a semiconductingdevice through electrical or magnetic fields.

The gate dielectric material that provides each gate dielectric materialportions 32A, 32B and 32C can be an oxide, nitride, and/or oxynitride.In one example, the gate dielectric material that provides each gatedielectric material portions 32A, 32B and 32C can be a high-k materialhaving a dielectric constant greater than silicon dioxide. Exemplaryhigh-k dielectrics include, but are not limited to, HfO₂, ZrO₂, La₂O₃,Al₂O₃, TiO₂, SrTiO₃, LaAlO₃, Y₂O₃, HfO_(x)N_(y), ZrO_(x)N_(y),La₂O_(x)N_(y), Al₂O_(x)N_(y), TiO_(x)N_(y), SrTiO_(x)N_(y),LaAlO_(x)N_(y), Y₂O_(x)N_(y), SiON, SiN_(X), a silicate thereof, and analloy thereof. Each value of x is independently from 0.5 to 3 and eachvalue of y is independently from 0 to 2. In some embodiments, amultilayered gate dielectric structure comprising different gatedielectric materials, e.g., silicon dioxide, and a high-k gatedielectric can be formed.

The gate dielectric material used in providing each gate dielectricmaterial portions 32A, 32B and 32C can be formed by any depositiontechnique including, for example, chemical vapor deposition (CVD),plasma enhanced chemical vapor deposition (PECVD), physical vapordeposition (PVD), sputtering, or atomic layer deposition. In someembodiments, a thermal process including, for example, thermal oxidationand/or thermal nitridation may be used in forming each gate dielectricmaterial portions 32A, 32B and 32C. When a different gate dielectricmaterial is used for the gate dielectric material portions 32A, 32B and32C, block mask technology can be used. In one embodiment of the presentapplication, the gate dielectric material used in providing each gatedielectric material portions 32A, 32B and 32C can have a thickness in arange from 1 nm to 10 nm. Other thicknesses that are lesser than orgreater than the aforementioned thickness range can also be employed forthe gate dielectric material.

Each gate conductor portion 34A, 34B and 34C comprises a gate conductormaterial. The gate conductor material used in providing each gateconductor portion 34A, 34B and 34C can include any conductive materialincluding, for example, doped polysilicon, an elemental metal (e.g.,tungsten, titanium, tantalum, aluminum, nickel, ruthenium, palladium andplatinum), an alloy of at least two elemental metals, an elemental metalnitride (e.g., tungsten nitride, aluminum nitride, and titaniumnitride), an elemental metal silicide (e.g., tungsten silicide, nickelsilicide, and titanium silicide) or multilayered combinations thereof.In some embodiments, the gate conductor material portion 34C andoptionally gate conductor material portion 34A may comprise an nFET gatemetal. In other embodiments, gate conductor material portion 34B andoptionally gate conductor material portion 34A may comprise a pFET gatemetal.

The gate conductor material used in providing each gate conductorportion 34A, 34B and 34C can be formed utilizing a deposition processincluding, for example, chemical vapor deposition (CVD), plasma enhancedchemical vapor deposition (PECVD), physical vapor deposition (PVD),sputtering, atomic layer deposition (ALD) or other like depositionprocesses. When a metal silicide is formed, a conventional silicidationprocess is employed.

When a different gate conductor material is used for gate conductorportion 34A, 34B and 34C, block mask technology can be used. In oneembodiment, the gate conductor material used in providing each gateconductor portion 34A, 34B and 34C has a thickness from 1 nm to 100 nm.Other thicknesses that are lesser than or greater than theaforementioned thickness range can also be employed for the gateconductor material used in providing each gate conductor portion 34A,34B and 34C.

Each gate conductor material and each gate material portion may bepatterned after formation thereof forming gate structures 30A, 30B and30C. A dielectric spacer material may then be formed on each gatestructure 30A, 30B and 30C and thereafter the dielectric spacer materialcan be etched to form dielectric spacers on exposed sidewall surfaces ofeach gate structure 30A, 30B and 30C.

Source/drain regions (not shown) can be formed in portions of eachsemiconductor fin, i.e., silicon fin 16, compressively strainedsilicon-containing germanium alloy fin portion 24 or tensile strainedsilicon-containing fin portion 28, that are not covered by either thegate structure or the dielectric spacer. The source/drain regions can beformed by introducing a dopant into the exposed portions of eachsemiconductor fin, i.e., silicon fin 16, compressively strainedsilicon-containing germanium alloy fin portion 24 or tensile strainedsilicon-containing fin portion 28, which are not covered by either thegate structure or the dielectric spacer. The dopant can be n-type orp-type. The term “p-type” refers to the addition of impurities to anintrinsic semiconductor that creates deficiencies of valence electrons.Examples of p-type dopants, i.e., impurities, include, but are notlimited to, boron, aluminum, gallium and indium. “N-type” refers to theaddition of impurities that contributes free electrons to an intrinsicsemiconductor. Examples of n-type dopants, i.e., impurities, include,but are not limited to, antimony, arsenic and phosphorous. In someembodiments, the dopant may be introduced into the exposed portions ofeach semiconductor fin, i.e., silicon fin 16, compressively strainedsilicon-containing germanium alloy fin portion 24 or tensile strainedsilicon-containing fin portion 28, by ion implantation, plasma doping orgas phase doping. The concentration of dopants used in providing thesource/drain regions can range from 5e18 atoms/cm³ to 1.5e21 atoms/cm³.

In some embodiments, the source/drain regions can be merged. The mergingof the source/drain regions can be provided by growing an epitaxialsemiconductor material utilizing an epitaxial growth process as definedabove. A dopant can be introduced into the epitaxial semiconductormaterial that is used to merge the various regions together eitherduring the epitaxial growth process itself, or following the epitaxialgrowth process by utilizing gas phase doping. The dopant concentrationof each of the merged regions is typically from 5e18 atoms/cm³ to 1.5e21atoms/cm³.

In some embodiments of the present application, region 100 can beomitted from the final structure.

While the present application has been particularly shown and describedwith respect to various embodiments thereof, it will be understood bythose skilled in the art that the foregoing and other changes in formsand details may be made without departing from the spirit and scope ofthe present application. It is therefore intended that the presentapplication not be limited to the exact forms and details described andillustrated, but fall within the scope of the appended claims.

What is claimed as new is:
 1. A method of forming a semiconductorstructure comprising: forming a plurality of silicon fins extendingupwards from a bulk silicon portion, wherein each silicon fin of saidplurality of silicon fins is separated by a trench isolation region;recessing a predetermined number of silicon fins of said plurality ofsilicon fins to provide a plurality of silicon fin portions in an nFETdevice region and a pFET device region of said bulk silicon portion;forming a relaxed silicon germanium alloy fin portion on a topmostsurface of each silicon fin portion; forming, in any order, acompressively strained silicon-containing germanium alloy fin portion ona topmost surface of each relaxed silicon germanium alloy fin portion insaid pFET device region and a tensile strained silicon-containing finportion on a topmost surface of each relaxed silicon germanium alloy finportion in said nFET device region; and recessing each trench isolationregion to provide trench isolation structures and to partially exposesidewall surfaces of each compressively strained silicon-containinggermanium alloy fin portion and each tensile stained silicon finportion, wherein some of said silicon fins are non-recessed and each ofsaid non-recessed silicon fins has a topmost surface that is coplanarwith a topmost surface of each of said compressively strainedsilicon-containing germanium alloy fin portion and said tensile strainedsilicon-containing fin portion, and wherein a low leakage functionalgate structure is formed on exposed sidewall surfaces and said topmostsurface of each of said non-recessed silicon fin.
 2. The method of claim1, wherein said forming said plurality of silicon fins extending upwardsfrom said bulk silicon portion comprises: providing a structureincluding, from bottom to top, a hard mask layer and a bulk siliconsubstrate; forming a plurality of trenches in said hard mask layer andsaid bulk silicon substrate; and filling each of said trenches with atrench dielectric material.
 3. The method of claim 2, wherein prior toperforming said etching process, a block mask is formed on some of thesilicon fins in a region of the bulk silicon portion other than saidnFET device region and said pFET device region.
 4. The method of claim1, wherein said recessing said predetermined number of silicon fins ofsaid plurality of silicon fins comprises an etching process.
 5. Themethod of claim 1, wherein said forming said relaxed silicon germaniumalloy fin portion comprises an epitaxial semiconductor regrowth process.6. The method of claim 5, wherein each relaxed silicon germanium alloyfin portion comprises a lower portion having a first defect density andan upper portion having a second defect density that is less than thefirst defect density.
 7. The method of claim 1, wherein said forming thecompressively strained silicon-containing germanium alloy fin portion isperformed prior to forming said tensile strained silicon-containing finportion and a block mask is used to protect the nFET device regionduring said forming of said compressively strained silicon-containinggermanium alloy fin portion.
 8. The method of claim 1, wherein saidforming the tensile strained silicon-containing fin portion is performedprior to forming said compressively strained silicon-containinggermanium alloy fin portion and a block mask is used to protect the pFETdevice region during said forming of said tensile strainedsilicon-containing fin portion.
 9. The method of claim 1, wherein saidforming said compressively strained silicon-containing germanium alloyfin portion comprises an epitaxial deposition process and said formingsaid tensile strained silicon-containing fin portion comprises anotherepitaxial deposition process.
 10. The method of claim 1, furthercomprising forming a functional gate structure on exposed sidewallsurfaces and a topmost surface of said compressively strainedsilicon-containing germanium alloy fin portion, and forming anotherfunctional gate structure on exposed sidewall surfaces and a topmostsurface of said tensile strained silicon-containing fin portion.
 11. Themethod of claim 2, wherein after forming said compressively strainedsilicon-containing germanium alloy fin portion and said forming saidtensile strained silicon-containing fin portion, said block mask isremoved to expose another predetermined number of silicon fins, andwherein after said recessing said trench isolation structures, a furtherfunctional gate structure is formed on exposed sidewall surfaces and atopmost surface of each silicon fin.
 12. The method of claim 1, whereinsaid compressively strained silicon-containing germanium alloy finportion, said relaxed silicon germanium alloy fin portion and saidsilicon fin portions in said pFET device region have sidewall surfacesthat are vertically coincident to each other.
 13. The method of claim 1,wherein said tensile strained silicon-containing fin portion, saidrelaxed silicon germanium alloy fin portion, and said silicon finportions in said nFET device region have sidewall surfaces that arevertically coincident to each other.
 14. The method of claim 1, whereineach relaxed silicon germanium alloy fin portion contains threadingdislocations.
 15. The method of claim 14, wherein said threadingdislocations in each of said relaxed silicon germanium alloy finportions terminate at a sidewall of one of said trench isolationstructures.
 16. The method of claim 1, wherein each relaxed silicongermanium alloy fin portion has a relaxation value of 90% or greater,and a germanium content of 20 atomic percent or greater.
 17. The methodof claim 1, wherein said compressively strained silicon-containinggermanium alloy fin portion contains a greater amount of germanium thansaid relaxed silicon germanium alloy fin portion in said pFET deviceregion.
 18. The method of claim 1, wherein said tensile strainedsilicon-containing fin portion consists of unalloyed silicon.
 19. Themethod of claim 1, wherein said tensile strained silicon-containing finportion consists of a silicon germanium alloy having a germanium contentthat is less than a germanium content of said relaxed silicon germaniumalloy fin portion in said nFET device region.
 20. A method of forming asemiconductor structure comprising: forming a plurality of silicon finsextending upwards from a bulk silicon portion, wherein each silicon finof said plurality of silicon fins is separated by a trench isolationregion; recessing a predetermined number of silicon fins of saidplurality of silicon fins to provide a plurality of silicon fin portionsin an nFET device region and a pFET device region of said bulk siliconportion; forming a relaxed silicon germanium alloy fin portion on atopmost surface of each silicon fin portion; forming, in any order, acompressively strained silicon-containing germanium alloy fin portion ona topmost surface of each relaxed silicon germanium alloy fin portion insaid pFET device region and a tensile strained silicon-containing finportion on a topmost surface of each relaxed silicon germanium alloy finportion in said nFET device region; and recessing each trench isolationregion to provide trench isolation structures and to partially exposesidewall surfaces of each compressively strained silicon-containinggermanium alloy fin portion and each tensile stained silicon finportion, wherein said tensile strained silicon-containing fin portionconsists of a silicon germanium alloy having a germanium content that isless than a germanium content of said relaxed silicon germanium alloyfin portion in said nFET device region.